Study On Residual Stress Of 316L/BNi-2 Brazed Joint Considering Element Diffusion

Plate-fin heat exchanger plays an important role in modern high-tech industry such as high-temperature gas-cooled reactor,large-scale petrochemical reaction unit and fuel cell.The reliability of plate-fin structure is the key to the safe operation of these components.The quality of the brazed joints is of the utmost importance.Therefore,it is of great significance to improve the mechanical properties of brazed joints and optimize the brazing process through studying the residual stress of brazed joints.Most of present studies are based on the elastoplastic constitutive model,in which the brazing process of the evolution of the joint region and the diffusion of elements are ignored.However,the residual stress of the brazed joints can not be assessed by using this method.To the above issues,from the point of the brazing process,the microstructure and the formation of the brazed joint are investigated.Then a multi-field coupled model is developed to study the residual stress of the plate-fin structure.The main contents and conclusions are as follows:(1)Based on SS316L/BNi-2 wedge joint samples,the effects of microstructure phase,hardness,DAZ layer thickness and MBC value were analyzed in detail,and the diffusion kinetic parameters of element B in DAZ layer were calculated.(2)In order to accurately study the residual stress of the brazed joint,the diffusion of elements is taken into account.Based on the microstructure of 316L/BNi-2 brazed joint at 1075℃ for 45min,the finite element model was established.The residual stress of the joint was simulated and measured by nanoindentation and XRD tests.The feasibility and accuracy of the finite element method were verified.(3)Based on the above theoretical and analytical ideas,the residual stress distribution in the plate-fin structures of the heat exchanger was studied by using the proposed finite element method.Then the effects of the structural parameters on residual stress distribution were further analyzed.These results will provide some theoretical guidance for the optimization of plate-fin heat exchangers and other equipment with similar structures.